var btn_login = document.getElementById('btn_login');
btn_login.onclick = function(){
    var account = document.getElementById('account');
    var pwd = document.getElementById('password');  
    var tip = document.getElementById('log_tip');
    if(account.value.length == 0 || pwd.value.length == 0){
        tip.innerHTML = "请输入用户名和密码";
        tip.className = 'tip_change login_tip';
    }else {
        document.getElementById('login_form').submit();
    }
}
